The present invention relates to audio signal processing, and more particularly relates to the processing of such signals to embed auxiliary data (e.g. identification or control data therein), and the subsequent extraction and use of such data.
The copying and redistribution of sound recordings has long been a cause of lost revenues to the creators/producers of such material. The advance of technology has not only expanded the means of legitimate distribution for audio works, but has also made it easier to copy these materials for unauthorized purposes.
Various methods have been developed to eliminate or limit both sophisticated and unsophisticated illegitimate distribution. Some of these methods rely on physical means. Others employ a xe2x80x9cdon""t copyxe2x80x9d signal to disable a machine""s recording function.
In accordance with preferred embodiments of the present invention, a multi-bit control message (sometimes termed a xe2x80x9cdigital watermarkxe2x80x9d) is embedded directly into the sample values of the audible portion of an audio signal. Hardware or software systems can then read this control message and, for example, disable recording functions if so instructed.
Key practical issues are addressed whereby the perceptual impact of this added message can be adjustedxe2x80x94both overall and as a function of the underlying audible content. For example, a quiet passage ought in general to have minimal added information, whereas loud passages can generally tolerate more added energy in a watermark.
Methods are further detailed whereby the embedded message can survive lossy compression processes. An example of a lossy compression process is the MPEG compression standard.